Remote Desktop into Windows From Ubuntu
 

Ok, I have a VNC server set up on my Windows box, but every attempt to connect to it fails. It's running RealVNC Server (user mode). I've tried with everything I've got. Would someone mind telling me step by step how to login to it?

verify that you're windows firewall is not blocking the port 5900 (i think that's defaul vnc for windows)

Maybe this might be easier:

Use Remote desktop sharing and share your Desktop under Windows XP.
Then use rdesktop to log in to your windows Box using rdp protocol.
I think it easier that way ;)